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From: oj@apollo.UUCP
Newsgroups: comp.windows.x
Subject: Re: Problem with motion event handling?
Message-ID: <3898d627.d5b2@apollo.uucp>
Date: Fri, 20-Nov-87 18:26:00 EST
Article-I.D.: apollo.3898d627.d5b2
Posted: Fri Nov 20 18:26:00 1987
Date-Received: Sun, 22-Nov-87 12:39:10 EST
References: <3312@aw.sei.cmu.edu>
Reply-To: oj@apollo.UUCP (Ellis Oliver Jones)
Organization: Apollo Computer, Chelmsford, MA
Lines: 74
Keywords: X11 motion events

In article <3312@aw.sei.cmu.edu> kwh@sei.cmu.edu (Kurt Hoyt) writes:
>
>..events while a button is down so I can move the object...
>Selecting ButtonMotionMask generates
>MotionNotifys whether or not a button is pressed.

Write xbugs on this, if you're absolutely sure it's happening, and you
haven't inadvertently selected PointerMotionMask.  Are the motion
events coming from some other window you've enabled them from?

> Selecting
>PointerMotionHintMask ONLY generates nothing. 
That's right;  PointerMotionHintMask is a modifier for
any of the masks that select motion events.

>Selecting either
>ButtonMotionMask or PointerMotionMask along with PointMotionHintMask will
>generate one MotionNotify if the pointer moves and no buttons are pressed
>and lots of MotionNotifys when any button is pressed (followed by one
>MotionNotify after the button is released). 

A little confusion here, I fear.
If you select ButtonMotionMask without PointerMotionMask, you
should not get MotionNotify events without any buttons held down.
Check the event.xmotion.state field for (Button1Mask|Button2Mask|Button3Mask...)
to be absolutely sure.

If you select PointerMotionMask, you should get MotionNotify events whenever
the pointer moves.

If you ALSO specify PointerMotionHintMask, you *may* get fewer
MotionNotify events.  These events should have the is_hint field set
to True.  To be perfectly correct, you must respond to each motion
hint with an XQueryPointer or XGetMotionEvents ; there's an optional
interlock capability.

I use this code fragment to respond to MotionNotify when I'm expecting hints;
it seems to work (on Xapollo).

XNextEvent ( dpy, &myevent);
...
case MotionNotify:
   /* spin through any excess MotionNotify events */
   while ( XCheckMaskEvent 
               (dpy, (PointerMotionMask | ButtonMotionMask), &myevent ));
   /* break interlock on MotionHint stuff */
   if (myevent.xmotion.is_hint)
           XQueryPointer (dpy, iw, &jw, &jw, &jw, &jw, &xxx, &yyy, &jw);
   else { xxx = myevent.xmotion.x;  yyy = myevent.xmotion.y; }

>XGetMotionEvents consistently
>has nothing to report (called initialliy with start = 0, stop =
>CurrentTime). 
That's right.   No servers yet do motion history buffers; motion history
buffers are optional on all servers.  To see if you have a motion history
buffer available, look at the Display field's motion history buffer. 

     Display * dpy;
    ...
     dpy->motion_buffer

If it's zero...you're out of luck on motion history buffers.

>Other selected events:  ExposureMask, ButtonPressMask, ButtonReleaseMask,
>KeyPressMask.

Note that funny things happen when you select ButtonPressMask without
also specifying OwnerGrabButtonMask.  The act of pressing the button
grabs the pointer;  this means that it gets a frozen event mask (except
due to the action of the OwnerGrabButtonMask).  So, if you were
trying to do another XSelectInput in response to the ButtonPress,
you were probably not seeing the mask change.

/oj